Orifice Sizing & Selection

Using Daniel Orifice CalculatorByMohd Shahriman B M Sharif

Supervised byEzatolah Mardasi

Daniel Orifice Calculator

Objectives of this exercise are to get the– a)Beta Ratio– b)Bore Diameter

Case StudyOperating Data

Applicationbarg3.2Upstream pressure

t/day432,840,1200Flow rate (min, norm, max)

40Schedule

Inches3Pipe Size Nom

Kg/m3996Density

WaterFluid

Unit

Water Tank

FT

3.2 Barg7.5 Barg

Orifice

What you should know. . .What is an orifice ?What is beta ratio ?What is bore size ?What is full scale flow ?What Differential Pressure (dP) to use ?What is a good beta ratio ?What is the relation between– DP vs Beta Ratio– Beta Ratio vs Bore Size– Beta Ratio vs Straight Line Requirements– Beta Ratio vs Permanent Pressure Loss

What to do next ?

What is an Orifice ?It is the simplest type of DP flow measurement deviceUse restriction to create differential pressure (DP) thus measuring flow.

What is Beta Ratio ?

Beta ratio is the ratio of the bore diameter (orifice ) to the inner diameter of the pipe

Beta Ratio= d/D

Flow

D d

What is “Full Scale Flow” ?Full scale flow is the value that we use to incorporate some “swing” margin for measuring the flow in all possible condition.

PTS 32.31.00.32 Section 4.7– For the scale reading, a round figure

should be selected that is 1-5% above the maximum flow to be measured under normal or abnormal operating conditions and 15-20% above the normal design flow. The scale reading is usually expressed in mass flow units.

Guru said :– Full scale flow (FSF) shall be of

» Round Figure» 30 % Above normal flow» 10% Above maximum flow

Full Scale Flow / Sizing Flow

MarginOperating Span

Min Norm FSF%

Choose which is highest

What is “Full Scale Flow”In our case:

{Minimum Normal Maximum } Flow

Full Scale Flow @ Sizing Flow

1200840432MaxNormMin

Turn down ratio:1200/432 =2.7

1200840432MaxNormMin

30% 10%840x1.3=1092 1200x1.1=1320Thus full scale flow= 1320

Note: We takethe highest

value

Differential Pressure (dP)According to PTS 32.31.00.32– To limit the static pressure loss, the calculated dP-range should

preferably be approximately 0-250 mbar. – Ranges lower than 0-12.5 mbar and higher than 0-1000 mbar

should be avoided.Therefore

Guru said, the dP shall be ...kPa inH20 mBar0-25 0-100 0-1250-50 0-200 0-2500-75 0-300 0-3750-100 0-400 0-5000-125 0-500 0-6250-150 0-600 0-7500-175 0-700 0-8750-200 0-800 0-1000

We move to thenext range whenbeta ratio is not

feasible

1-Select

2-Density

3-Pipe Size

4-Flow Rate

5-Diff Pressure

Using the software

Opps ...we have warning . . .

What is a good beta ratio?The normal practice will say that a good beta ratio lies in between 0.2 to 0.7, but when we size the orifice, we will try to get the beta ratio to be in the range of 0.4 to 0.5 (in the middle). Guru said

• in between 0.2 to 0.7 normal• in between 0.4 to 0.5 the best

BUT , this value will depend on the case to case basis in term of the piping isometric e.g elbow and straight run space available.In our case, the value is more than the recommended beta ratio (0.2 to 0.7) . Let see what will happen if we increase the dP further.Note :Increasing the dP will increases the accuracy of the F.E BUT at the same time increasing the permanent pressure loss downstream.

What will happen next ?DP(mBar) Beta(d/D) Bore Size(inch)

250 0.75265 2.309300 0.72906 2.237350 0.70876 2.174400 0.69101 2.12450 0.67528 2.072500 0.66119 2.029550 0.64845 1.989600 0.63686 1.954650 0.62623 1.921700 0.61644 1.891750 0.60736 1.863800 0.59892 1.837850 0.5913 1.813900 0.58364 1.791950 0.57668 1.7691000 0.57013 1.749

Beta(d/D) Vs DP (mBar)

0.50.55

0.60.65

0.70.75

0.8

0 500 1000

Beta(d/D)

Bore Size(inch)

1.51.71.92.12.32.5

0 500 1000

Bore Size(inch)

As dP increase, the beta ratio &the bore size

reduces

Beta Ratio vs Bore SizeAs beta ratio bore size

Let D= 1(Fixed), d= X

Bore Size(inch)

1.51.71.92.12.32.5

0 500 1000

Bore Size(inch)

Logically, to create more dP more

restriction is needed

Beta=X/1

1 X

Straight line requirements

From ISO 5167-1

* Values include 0.5% additional uncertainty* Value are for simple case of single 90 degrees bend or tee (flow from one branch only)

As beta ratio increases the problem will lies in the straight line requirement

needed. Example at the maximum beta ratiothe upstream requirement is 14D

and downstream requirement is 3.5D

4230.8

4180.75

3.5140.7

3.5110.65

3.590.6

380.55

370.5

370.45

370.4

2.560.35

2.560.3

260.25

260.2

DownstreamUpstreamBeta

So what do we choose ?DP(mBar) Beta(d/D) Bore Size(inch)

250 0.75265 2.309300 0.72906 2.237350 0.70876 2.174400 0.69101 2.12450 0.67528 2.072500 0.66119 2.029550 0.64845 1.989600 0.63686 1.954650 0.62623 1.921700 0.61644 1.891750 0.60736 1.863800 0.59892 1.837850 0.5913 1.813900 0.58364 1.791950 0.57668 1.7691000 0.57013 1.749

Beta > 0.7

Beta < 0.7

At down stream 65% of up stream dP is loss.E.g at 500mBar Loss=325mBar

Thus we choose :dP = 400mBarBeta = 0.69101Bore = 2.12

What we do now ?We have– Beta Ratio– Bore Size– dP

We also need to have– Material– Plate Thickness– Concentricity– Finish of throat– Finish of plate– Vent/Drain hole– Welding of tab

We can calculate any of these parameters as long as two parameters are given

From Orifice Standard Drawing S.32.114

Concentric,Eccentric & Segmental

Concentric Eccentric Segmental

Normally use for clean fluids

Liquid containing gas

Vapour containing liquid or liquid containing solids

Concentric

Squared/Sharp Edge

Quadrant Edge

Conical Edge

-Use with flange tap or corner tap-To assist in creating Vena Contracta on viscous fluids

-Use with ONLY corner tap-To assist in creating Vena Contracta on viscous fluids

FLOW

FLOW

FLOW

Square/Quadrant/Conical Edge

Selection mainly governs byVISCOCITY

-Use to recover pressure drop after Vena Contracta

Summary . . .

Orifice Type Edge Type

Appropriate Process Fluid

Reynolds Number Range

Normal Pipe Size

(Inches)Concentric Square Edge Clean gas or liquid >2000 1-60Concentric QuadrantConcentric Conical EdgeEccentric

Segmental

1-6Viscous, Clean liquids

Square Edge Dirty gas or liquid

200-10 000

>10 000 4-14

Pressure Tapping

1

2 3

4

:: Flange Tapping :: Commonly use

:: D & D/2 Tapping or 2 1/2D & 8D (use in USA) :: Use for line >12’’ due to flange cost

:: Corner Tapping :: Spacing between the centerline of the plate equal to half diameter or half of width of the tapping

FLOW FLOWD

D D/2 2 1/2 D 8D

FLOW

1

2 3

4

Limits of Orifice Combinations

Orifice/ Pressure Tapping

Beta Ratio Bore 'd' (mm) Reynolds No Normal Pipe

Size(mm)

Square Edgewith

Flange TapsSquare Edge Re>5e3 for B<0.45

with Re>5e3 for0.45<B<0.77Corner Taps Re>2e3 for 0.77 <BConical Edge

withCorner Taps

Re>1260*B*D

Re>250*B

50<D<760

50<D<1000

D>25 No upper limits

0.2<B<0.75

0.23<B<0.8

0.1<B<0.136

d>12.5

d>12.5

d>6.0

Source ISO 5167-1

ConclusionRelationship– DP vs Beta Ratio

• As DP increases Beta Ratio decreases– Beta Ratio vs Bore Size

• As Beta Ratio increases bore size increases– Beta Ratio vs Straight Line Requirements

• As Beta Ratio increases straight line requirements increases– Beta Ratio vs Permanent Pressure Loss

• As Beta Ratio increases,dP increases thus more permanent pressure loss downstream

Sizing– Take the dP which is closest to 0-25KPa range– Beta ratio should be around 0.4 to 0.5 but depends on application– Consider the permanent pressure loss upstream at that dP– Consider the straight line requirement– Consider the TX range needed for that dP

THANK YOU

Orifice Standard Drawing S.32.114